Microsoft's new browser, Internet Explorer 10 (IE10), will not run on Windows Vista, either now in its developer preview form or when the software ships, the company confirmed today.

Microsoft follows pattern it set last year when it denied IE9 to XP users, says IE10 is only for Windows 7

Microsoft's new browser, Internet Explorer 10 (IE10), will not run on Windows Vista, either now in its developer preview form or when the software ships, the company confirmed today.

The decision makes Microsoft the first browser developer to drop support for Vista, and follows the move last year when it announced Windows XP would not run IE9, the browser that went final four weeks ago.

In release notes published Tuesday, Microsoft said that users need to run the IE10 Platform Preview on Windows 7 RTW -- the designation for the original 2009 release of the OS -- or Windows 7 Service Pack 1 (SP1). The latter started reaching users on Feb. 22.

Windows 7 RTW must be updated before it's able to run IE10, said Microsoft.

When Vista users try to install the IE10 preview, they see a dialog box that reads, "Windows Internet Explorer Platform Preview does not support any operating system earlier than Windows 7," after which the installation process terminates.

Windows XP users see the same message when they attempt to install IE10.

Wednesday, Microsoft confirmed that the new browser is intended only for Windows 7.

"Windows Vista customers have a great browsing experience with IE9, but in building IE10 we are focused on continuing to drive the kind of innovation that only happens when you take advantage of the ongoing improvements in modern operating systems and modern hardware," a Microsoft spokeswoman said in an email reply to questions.

The spokeswoman also lumped Vista in with the 10-year-old Windows XP when asked why Microsoft was abandoning the former with IE10.

"Regarding Windows Vista, our decision with IE9 was not to build to the lowest common denominator," she said. "With IE9 we made the decision to help unlock the best Web experience possible, which means taking advantage of everything around the browser -- including Windows 7 and modern PC hardware."

Microsoft has been aggressively promoting the idea that a browser is only as good as the operating system it runs on, and that by extension, browsers that run on older OSes are sub-standard.

Last month, Dean Hachamovitch, who leads the IE team, went so far as to say that rivals -- presumably meaning Google and Mozilla -- "dilute their engineering investments" by creating browsers for the Mac, Linux and Windows XP.

Vista users were unhappy about the news that their machines won't run IE10.

"IE10 is not supported for Vista? Looks like IE9 is the new IE6," said one commenter, labeled only as "IE9 is the new IE6."

Try to install IE10 Platform Preview on Windows Vista and this dialog appears.

"Yes, Vista has a bad image, but still it's supported and falls within the product life cycle," added another commenter . "Not supporting Vista will send a BAD signal."

According to Web metrics company Net Applications, Windows 7 held a 24% share last month. Windows XP, with 54%, and Vista, with 11%, accounted for two-thirds of all operating systems.

Christian Kane, a researcher with Forrester Research who covers browsers, said Microsoft's move "made sense" because of Vista's poor showing and that OS's gradual decline in use.

Forrester's figures had Vista topping out at a 15% share of the enterprise market, and shrinking since then. "And most companies now see Vista as a stepping stone to Windows 7," Kane said.

Twenty percent of Forrester's corporate clients are now running Windows 7, he added.

"Microsoft wants to get everyone on Windows 7," said Kane, and excluding IE10 from other editions of Windows is part of that strategy. "This shows Microsoft's long-term commitment to Windows 7. I don't see it as shortsighted at all."

Other browser makers, most notably Firefox developer Mozilla, have blasted Microsoft for abandoning XP, saying that it's possible to tack on some support in the aged OS for hardware acceleration, the feature that Microsoft said drove it to ignore XP with IE9.

Google, whose Chrome also runs on both XP and Vista, did not reply to a request for comment today on Microsoft's IE10 decision. Mozilla declined to comment.